<!DOCTYPE html>
<title>&lt;semantics&gt - mozilla bug 21479 (reference)</title>
<meta charset="utf-8"/>
<p>
  <math xmlns="http://www.w3.org/1998/Math/MathML">
    <mover>
      <mspace width="300px" height="10px" mathbackground="black"></mspace>
      <mo>&#xaf;</mo>
    </mover>
  </math>
</p>
